it is assumed that the user will specify the desired archive_command in the postgresql_parameters variable, example:

postgresql_parameters:
  - { option: "archive_command", value: "{{ pgbackrest_archive_command }}" }
  - ...

But if he didn't do it explicitly, then we substitute him at the pre-checks level - https://github.com/vitabaks/autobase/blob/2.4.1/automation/roles/pre_checks/tasks/pgbackrest.yml

it is assumed that the user will specify the desired archive_command in the postgresql_parameters variable

Ah! Though I am not sure if this is best approach:

• Doing so is non-intuitive, especially if there are dedicated pgbackrest_* vars available including the pgbackrest_archive_command
• pgbackrest_archive_command seems to be a no-op right now. If it shouldn't be used at all, it should be removed.

I personally try to avoid setting postgresql_parameters as it requires adding the full default definition into my group_vars, as otherwise these params aren't set anymore. However, this also means I can't easily spot anymore which of these I've now actually changed and which ones are defaults. This is a known issue with (long) variable list definitions in Ansible.

From a user PoV, I'd highly prefer pgbackrest_archive_command being respected (if set). This is what this PR is doing.
I see it duplicates code in some ways but in the end it just ensure a proper use of the var in the first place. Maybe there are better ways but I don't think the current way is a good approach in the longterm.

I'm thinking of adding a postgresql_archive_command variable that will dynamically substitute a value based on which backup tool is being used, and use this variable as the value of the archive_command option.

That might be an option yes. From a user PoV, I'd be happy not having to set postgresql_archive_command or pgbackrest_archive_command unless I really want to put something modified there.

The best would be to have a default for backups in place and even when deciding for another tool, only having to use <tool name>_enabled: true or similar to use it.